Various attempts have been made to improve on the performance of the .50 BMG and 12.7mm Russian from time to time, for several reasons: to improve armour-piercing capability; to increase the effective range of AA guns; or to achieve a higher velocity to improve the hit probability of aircraft guns. However, few have been successful, and only one has survived to the present day: the formidable Russian 14.5x114 round used in the KPV.

.50 Vickers HV

The first attempt, the .5 Vickers HV (High Velocity) for the Class D machine gun, was only a marginal improvement over the contemporary .50 BMG because its starting point was the much less powerful .5 Vickers (12.7x81) described in Part 1. It was developed in the 1920s in parallel with the smaller round, but enjoyed little success.

The gun was basically a lengthened version of the usual .5 inch Vickers, designed around a much bigger and more powerful 12.7x120SR cartridge, known as the V/664 (with 664 grain flat-based bullets) or V/ 690 (690 grain boat-tailed - streamlined - bullets); the heavier bullet became the standard type. This round achieved a muzzle velocity of 3,040 fps. Bullet types developed for both the V/664 and V/690 were Ball, AP, AP-T, Flame Tracer, and Smoke Tracer/Incendiary. Maximum range claimed was 7,000 yards with a vertical altitude of 15,600 feet but, as with the 12.7x81, effective ranges would have been far less; probably 1,000 yards in AA fire and double that against ground targets.

The gun barrel was water-cooled, as was usual for a Vickers, and the rate of fire was 350-450 rpm. Gun weight was 101 lbs, or 122 lbs with water, and it was noticeably longer than the compact Class B, with a barrel length of 45 inches and an overall length of nearly six feet. This was offered primarily as an AA gun in a twin mounting, or as an AT gun in a single mounting, although both mountings could be used in either role. The single mounting, complete with water, weighed 623 lbs while the twin weighed just over a ton in action.

Despite various experiments (including installing a twin mounting on a Vickers Light Tank Mk 1A) the Class D was never fielded by Britain. It did achieve some very limited foreign sales; Siam bought 24, China 20 and Japan 48.

15mm ZB vz 60 (BESA)

The 15mm ZB vz 60 (Zbrojovka Brno vzor 60, the name of the factory in Brno and the model number) was originally designed as a 20mm gun and successfully tested in 1933, but the Czech Army rejected it and demanded an HMG instead; originally in 14.5mm calibre, later increased to 15mm. By the late 1930s the design had been finalised around a powerful 15x104 cartridge. The gun was beltfed, 6 feet 9 inches long, weighed 121 lbs and fired at 420 rpm.

The big ZB was used as an AA weapon by Czechoslovakia and Yugoslavia and taken over in quantity by Germany, who shortened the case to 101mm in order to accept the longer projectiles from the MG151 aircraft gun ammunition. It was also adopted by the UK just before the Second World War, as the 15mm Besa (named after the British maker, Birmingham Small Arms or B.S.A.), to replace the .5 inch Vickers in light Armoured Fighting Vehicles. However, it was never popular as its size made it difficult to handle in the cramped and unpowered turrets of the light tanks and armoured cars which used it. Some thought was given by the British to converting it to use 20mm Hispano ammunition (the diameter of the cartridge case was the same), but this did not succeed.

15mm MG 151

The MG 151 was designed as an aircraft gun by Mauser in the late 1930s. It was first developed in 15x96 calibre, and in this form was considerably more powerful than any other aircraft HMG to see service. It was a contemporary of the 20mm Hispano and fired a cartridge with a high-capacity case, which was coincidentally virtually the same diameter as the Hispano’s. As with all of the later German aircraft guns, the MG 151 was available with electric priming to facilitate synchronization (this version being sometimes referred to as the MG 151E), although percussion-primed versions were developed first.

Armour penetration of the AP shot was 18mm/330 yards/60°; there was a tungstencored AP (Hartkernmunition) loading reserved for use against armoured vehicles; it could penetrate up to 42mm at 330 yards.

The 15mm gun was first fitted to the Bf 109F in 1941 and was also carried by several other aircraft. However, wartime experience revealed that a larger explosive shell was more valuable than very high velocity, so the MG 151 cartridge case was“necked out” and shortened (to preserve the same overall cartridge length) to use the 20mm shells of the MG-FFM cannon, creating the 20x82 cartridge and the MG 151/20 gun. Projectile weight went up at the expense of muzzle velocity, but the gun weight of 93 lbs and rate of fire of around 700 rpm remained the same. This gun and the 20mm ammunition are still in production in South Africa, but the 15mm version did not survive the end of the war.

14.5mm KPV

In the late 1930s the Soviet Union made various attempts to develop an effective anti-tank rifle. Their first effort, the Sholoklov, was a variant of the First World War boltaction Mauser M1918 chambered for the Soviet 12.7x108 HMG cartridge described in Part 1. This proved inadequate, so a very powerful new cartridge was developed, the 14.5x114, and two rifles designed around it eventually saw service: the semiautomatic PTRS and the more popular manuallyloaded PTRD. The development of an HMG to chamber the new round started as early as 1942, with the first working prototypes being tested in 1944. Further development of the new gun, designated KPV (Krupnokalibernyj Pulemet Vladimirova - Vladimirov large caliber MG, after the designer) saw its adoption in 1949.

The KPV has had two major applications; as an Left: 15mm ZB vz60, the figure showing the massive size of the gun. AA weapon on towed mountings known as ZPU-1, -2 or -4, depending on the number of guns fitted, and as an armoured vehicle gun, typically mounted in turrets in various light AFVs. ZPU stands for Zenitnaya Pulemet Ustanovka, or AA machine gun system. ZPU-2 mountings were also fitted to light SPAAGs such as the BTR40B 4x4 and the BTR152A 6x6 and have proved useful in repelling convoy ambushes in Chechnya.

The high muzzle velocity coupled with a heavy projectile gives a performance in a different league from the 12.7mm and the .50 BMG. It has an effective ceiling of 4,600 feet, a horizontal range of 8,750 yards and the AP shot can penetrate 32mm of armour at 500m. Modern loadings include the Russian MDZ-M HEI round and a Chinese APDS.

This article first appeared in Small Arms Review V10N10 (July 2007)and was posted online on November 30, 2012